Typical coalescing filters are employed to separate liquid out of a gas stream containing a liquid component. As the gas passes through the filter, the liquid component is captured and coalesced by the filter. As more and more of the liquid component is captured, the droplets that are captured combine to form larger droplets. When the coalesced droplets are sufficiently large, gravity will allow the large droplets to exit the filter.
Coalescing filters have good separation efficiency for removing oil droplets from air stream. At the same time, most coalescing filters have significant pressure drop, which represents the energy expenditure. Usually, filters having higher separation efficiency also have higher pressure drop. This occurs because the filter loads up with liquid droplets. The liquid droplets occupy the porous space inside the filter medium; therefore, the filter media becomes saturated with the liquid load-up, which causes the pressure drop of the filter medium to increase.
In order to effectively continue the gas flow through the filter, the captured liquid must move through the filter and ultimately exit the filter, because the coalesced liquid reduces the pore space available for gas flow and thus causes an increase in pressure drop. To aid in the draining of the coalesced droplets, filters have been designed that utilize drainage channels at the inlet or outlet surfaces of the filters.
These drainage channels collect the coalesced liquid and drain it to an exit location. However, these filters often experience issues with liquid drainage and hold-up. Filters that do not effectively drain the coalesced liquid experience distorted gas flows, causing localized filter plugging and reducing the life of the filter.
Some coalescing filters include layers having different fiber properties, such as fiber diameter and surface energy. However, these filters often experiences issues with the liquid droplets being re-entrained into the gas flow. These filters also do not always provide sufficient pressure drop and flow characteristics.
Thus, a need in the art exists for an improved coalescing filter. The current invention is an improved coalescing filter that offers improved drainage, which results in more effective pressure drop and flow characteristics. According to the present invention, a coalescing filter is provided that comprises a drainage channel that extends at a downward angle, where the drainage channel has a higher porosity than the coalescing filter medium.